Conventional powertrain mounting systems generally operate to provide engine isolation and concurrently control engine motion. One common type of engine mount, the elastomeric engine mount, provides a fairly constant dynamic properties (e.g. elastic (K′) and loss (K″) rates) across the range of frequencies typically encountered in a specified application. The level of damping is generally increased or decreased by preselecting an elastomeric material having different properties and/or dimensions. Once constructed, set damping rate characteristics are provided regardless of the actual operating conditions encountered by the mount.
Hydraulic mounts were developed, in part, due to the desirability of providing a mount having a high damping coefficient for relatively high amplitude inputs and a relatively low damping coefficient for lower amplitude inputs. A typical hydraulic mount includes a pumping chamber enclosed by relatively thick elastomeric walls having an orifice track opening to the chamber and extending to a reservoir that is typically bounded by a flexible diaphragm. The reservoir is typically located on the opposite side of a partition from the pumping chamber. During compression, fluid is pressurized in the pumping chamber and flows through the orifice track to the reservoir. During rebound, fluid is drawn back to the pumping chamber from the reservoir. Mount dynamic stiffness and damping performance are determined by characteristics such as, for example, pumping chamber geometry, chamber wall material, and orifice track properties.
Additional increases in the performance characteristics of hydraulic mounts at selected frequency ranges were achieved by employing electronic control of the dynamic characteristics of the mount. This provided a preprogrammed ability to change the response of the mount to optimize dynamic performance. For example, in one known type of electronically controlled mount, a solenoid varies an orifice to provide fluid flow control between the pumping chamber and the reservoir of the mounts. In addition, engine mounting systems utilizing vacuum-driven switchable liquid-filled engine mounts were developed to provide different dynamic characteristics by selectively introducing into the chambers of the mount either (1) a vacuum from the intake manifold of an engine or (2) atmospheric pressure. Thus far, however, such engine mounts are capable of assuming only two states of dynamic stiffness and damping.
It would therefore be desirable to provide a switchable engine mount capable of providing at least three distinctive states with unique dynamic characteristics for use in an improved switchable powertrain mounting system. Furthermore, it would be desirable to provide a switchable powertrain mounting system that provides at least three selectable distinctive states based on the operating conditions of the vehicle. Other desirable features and characteristics will become apparent from the following detailed description taken in conjunction with the accompanying drawings and the foregoing technical field and background.